Long ago, I got in the habit of using Merriam-Webster's online dictionary. And I've suffered through the painfully slow page loads for the better part of a decade. But then I stumbled upon a better alternative. NinjaWords is "a really fast dictionary ... fast like a Ninja." Give it a try. You'll enjoy the speed.
PS Another cool option is Definr.com, which is fast and features a handy auto-complete function. Thanks to a reader for flagging that one for us.